Saiya-jn, since you attacked with multple rapid, small ki-burst questions, I shall counterattack in similar fashion...
2. Your OS/Apps drive will be incredibly fast with a single Raptor WD740GD; there is virtually zero benefit from running RAID 0 on a volume whose purposes is to serve up lot sof tiny files very quickly; the extremely short desktop access times of the Raptor already take care of that. For your A/V array, four 80GB Samsungs in RAID 0 with a larger stripe size, say 64-256KB, will outperform dual 160s. Four SP0812Ns and a single WD740GD together will still operate more quietly than dual WD740GDs and dual SP1614Ns. I'm assuming you need that much capacity; if you don't need a whole 320GB for A/V storage, consider using just a pair of SP0812Ns or three SP0812Ns; the fewer the number of platters per drive, the lower the acoustics is per drive.
3. For your CPU cooler, see if Thermalright's XP-120 fits your board; if it does, use it in conjunction with a Globe 120mm fan from MNPC-Tech.
It's the same as an AcoustiFan AF120CT (made by Globe), with the thermal control and everything, at 1/3 the price, and without the risk of getting a bad sample (there have been numerous reports of inconsistent manufacturing on the 120mm AcoustiFan).
If you plan to use a heatpipe cooler/isolator, the ZM-2HC2 is newer and better than the ZM-2HC1. I only recommend using one, for the one Raptor. For the Samsungs, suspend them using something like StretchMagic or bungee cord, and then blow a slow rotation fan across them like an undervolted Panaflo.
Your original graphics adapter choice with the Dual DVI outputs is a supremely wise choice. Do not settle for anything non-dual-DVI if you plan to use a pair of LCD flat panel displays that both have DVI connections. The difference in performance from analogue and digital with, "gamer," cards is immediately obvious. Only with a Matrox adapter would I ever consider driving an LCD, that offers DVI, analogue. I would be extra careful, however, to make sure that the NV Silencer 5 does, indeed, fit standard 6800s, particularly one that has been modified to fit dual DVI ports (to what extent it has been modified to do so, I am unsure). The reason being that while 6800GT and Ultra have almost the same exact PCB configuration (GT has Ultra's PCB but is missing some PWM components and a molex connector), the standard 6800 is a shorter card, so a cooler designed for GT/Ultra may or may not fit standard 6800.
Because you will be building a higher-draw-than-average machine, I would not recommend going the fanless PSU route, particularly considering the sheer number of hard drives. Getting something like a SeaSonic Super Silencer or Super Tornado and then swapping the stock fan for something like an undervolted Panaflo will not only be much safer and cooler running (particularly if you do a ducted Super Silencer), but it won't be a noticeable noise increase over the din of all those hard drives. Configured as I have described to you, the thing making the most noise is the 3-5 hard drives. A PSU with a Panaflo will not be audible over those drives, anyway.
How important is the portability/weight factor of this build? If that's not important, then I recommend sticking with steel cases, especially
with this many hard drives, an aluminum case will shake, rattle and roll many magnitudes more than a comparable steel case. Please put together a shopping list of steel cases you may be interested in (assuming portability is not paramount), and I can help you decide on a final one. Again, do spend the money on SilenX or AcoustiFan for 120mm; just buy Globe 120.
Nothing wrong with any of the LCDs you picked, as far as I can tell. I'm personally using a Hitachi CML175SXW and am extremely happy with it; it blows away my old Samsung 151P by a long shot.
Your original RAM choice is far superior to this Kingston stuff. I'm using the very same OCZ pieces on Gamma Three and love it.
I'm assuming you will be gaming, so the Audigy 2 ZS is likely the best choice possible, as its full support for EAX4 and even the upcoming EAX5 formats will be unmatched by any other brand card for a long time.
Anybody who has the money for a DiNovo and is willing to spend it should do it. Nothing else compares, including anything Gyration tries to put out.
My recommendations here focused on price first, performance second and acoustics last, but it improves upon all three fields, in general, over your original arrangement. Good luck and keep researching. There is no reason to spend as much money as you originally planned, particularly if superior acoustics and performance are already within reach for less (money).
You may yet become Supa' Saiya-jin before you know it!
EDIT: Straker's comments in regards to dual-channel is extremely good. For the time being, it's really not worth it to spend the additional loot on dual channel for K8; the performance difference does not justify the cost, particularly with PCI-Express boards on the horizon. Buy a single channel K8 arrangement now, and then when PCI Express K8 platforms are out and mature, it may then
be worth the cheese to upgrade, particularly since the K8 PCI-Express platforms will support multiple PCI-Express 16X slots (although primarily they're, "just," dual 8X slots with 16X form factors), but it would allow for SLI and that
be much more noticeable than dual channel on your K8!